The present invention relates to a method and apparatus for injecting and withdrawing coiled tubing into and from a well bore. More particularly, the system injects coiled and stalked tubing into a well bore from a tubing storage source or device and withdraws the tubing from the well bore and returns it to the storage source.
Devices and methods for injecting coiled tubing into and retrieving it from wells are well known. Previous injection systems are described in U.S. Pat. Nos. 6,142,406; 5,842,530; 5,839,514; 5,553,668; 5,309,990;. 5,244,046; 5,234,053; 5,188,174; 5,094,340; 4,899,823; 4,673,035; 4,655,291; 4,585,061; and other similar disclosures. Tubing injectors are used to grip and control the injection and withdrawal of the tubing at the wellhead. However, certain limitations influence the efficiency of the injection and withdrawal processes. One particular problem is the drag of the injected tubing along the inner walls of the drilled hole or casing resulting from the presence of residual curvature in the coiled tubing after its passage through the injector when it is being inserted into the well. As a result of this drag, additional injection forces must be applied to the tubing both to inject and to withdraw the tubing.
Conventional track injectors utilize gripper blocks mounted on two continuous parallel and opposed conveyor chains which are urged or pushed against the outer surface of the tubing. The interface forces between the gripper blocks and the tubing permit developing frictional forces which are used to transfer tangential loads from the conveyor chains to the tubing and vice versa. If insufficient interface force is applied to the tubing by the gripper blocks, slippage with attendant loss of control and wear occurs between the blocks and tubing. If excessive interface force is applied to the tubing by the gripper blocks, the tubing wall may be distorted and damaged or the injector may be damaged.
Historically, the approach used to increase the injection forces with conventional track injectors has been to lengthen the injector while maintaining a sufficiently safe interface force between the individual gripper blocks and the tubing. U.S. Pat. No. 5,842,530 for example shows provision of substantially more gripper blocks along the length of its injector.
Other injectors utilizing two continuous, parallel, and opposing track injectors having grooved shoes or blocks mounted thereon are known in the art. These opposing track units have facing portions where the multiplicity of gripping blocks run parallel for gripping the tubing therebetween and are typically positioned in line, directly adjacent and above the wellhead.
Another approach has been to utilize a large diameter driven wheel with an annularly grooved outer diameter to conform to and support the tubing. Hold-down idler rollers radially press the tubing against the wheel to provide extra interface force between the tubing and the wheel so that high tangential frictional forces can be imparted to the tubing by the wheel. While the mechanism of wheel type injectors is simple, inexpensive, and reliable, wheel size can be a limitation, especially for larger tubing diameters. One such wheel type injector is disclosed in U.S. Pat. No. 5,839,514.
A more recent injector system known in the art is a linear injector which pulls on only one side of the tubing. For this type of device, coiled tubing is driven along a single linear section of an endless chain conveyor with an opposing linear array of hold-down idler rollers. Such a linear or one-track injector eliminates the necessity of synchronizing the two opposed sides of a conventional track type injector and is less damaging to the surface of the coiled tubing, but it requires a much longer unit, which of necessity extends much higher and requires additional overhead clearance. Additionally, such an injector is more expensive because it requires a considerable number of gripper blocks and rollers and a longer support track.
There remains an existing need for an improved injector that can reduce damage to the surface of the coiled tubing while allowing an easier means for changing out the tubing size.
The present invention utilizes a novel approach to imparting tangential injection forces to the tubing. The driving means of this invention provides full support around the circumference of the tubing. By using a plurality of sets of opposed individually driven annularly grooved rollers which closely conform to the tubing and alternating the orientations of adjacent roller sets so that they are 90xc2x0 apart about the through axis of the injector, excellent tubing support is provided. The tubing injector of the present invention is light weight and compact and can fit with the other components for the injection system onto a truck, a trailer, or a skid.
One aspect of the present invention is a traction drive unit for imparting axial loads to tubing, the drive unit includes:
(a) a pair of drive modules, each drive module comprising a housing having a central window, an independent drive motor with an output shaft, and a roller having a circumferential annular groove aligned with the central window of the housing, the roller supported by rotary bearings and driven by the output shaft of said drive motor, wherein the rollers of the pair of drive modules are opposed and independently driven; and
(b) biasing means for independently urging the roller of each drive module into engagement with a tubing supported by the opposed rollers. Another aspect of the present invention is a tubing injector comprising:
(a) a traction drive unit for imparting axial loads to tubing, the drive unit having a plurality of pairs of drive modules, where each drive module includes a housing, an independent drive motor with an output shaft, and a bearing-supported roller in contact with a tubing, the roller driven by the output shaft of the drive motor such that each pair of drive modules have opposed and independently driven rollers;
(b) tensioning means for independently controlling the axial load applied to the tubing by each roller; and
(c) an injector housing, wherein the pairs of drive modules are mounted in the injector housing in an alternating pattern 90xc2x0 apart along an axis of the injector housing.
Yet another aspect of the present invention is an arc corrector having:
(a) a plurality of flex modules, each flex module having
(i) a tubular housing having a tube axis;
(ii) a pair of independently inwardly biased independently driven drive modules, said drive modules having a module housing, an independent drive motor with an output shaft, and a bearing-supported roller driven by the output shaft of the drive motor;
(iii) biasing means for independently urging the roller of each drive module into engagement with a tubing supported by the opposed rollers;
(iv) a plurality of coaxial linking pin holes perpendicular to and intersecting the housing tubing axis; and
(v) two cylinder mounting eyes located off the housing tube axis perpendicular to the plane defined by the linking pin hole axes and equispaced from the transverse midplane of the housing;
(b) a plurality of linking pins, wherein one linking pin engages one linking pin hole in each of two adjoining flex modules to interconnect the adjoining flex modules; and
(c) a plurality of hydraulic cylinders, the cylinders cojoining the cylinder mounting eyes of adjacent flex modules, wherein selective application of pressure to the hydraulic cylinders between interlinked flex modules imparts a change in curvature to the tubing supported by the opposed rollers of the flex modules.
The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.